The present invention relates to an optical transmission and reception device to be used in bidirectional communications, and in transmission of optical parallel link data in computers, and a method for fabricating the same.
Semiconductor lasers have been conventionally used as optical transmission and reception devices to be used in bidirectional communications in optical subscribers' systems, and as optical transmission and reception devices to be used in transmissions of optical parallel link data in computers.
A semiconductor laser conventionally used as an optical transmission and reception device will be explained with reference to FIG. 1.
An n-InP substrate 200 has the upper portion formed in the shape of a mesa, and an active layer 212 of InGaAsP is formed on the top of the mesa. The mesa is buried with a p-InP layer 202. An n-InP layer 204 is formed on the top of the p-InP layer 202 except the top of the active layer 212. A p-InP layer 206 is formed on the tops of the n-InP layer 204 and the active layer 212. The p-InP layer 202, the n-Inp layer 204 and the p-Inp layer 206 constitute a current blocking layer.
A contact layer 209 of p-InGaAsP is formed on the p-InP layer 206. A silicon oxide film 210 is formed on the contact layer 208, and a positive electrode 210 is formed on the top of the silicon oxide film 210, and a negative electrode 214 is formed on the underside of an n-InP substrate.
In using this conventional semiconductor laser of such structure as an optical transmission and reception device, on an optical transmission, the semiconductor laser is caused to emit light, and, on an optical reception, the semiconductor laser is supplied with a reverse bias voltage to serve as an optical receiver.
But the above-described optical transmission and reception device has the following drawbacks.
The above-described optical transmission and reception device is intrinsically a semiconductor laser having an optimum structure for a transmitter (light emitter), but does not have an optimum structure for a light detector. Accordingly the semiconductor laser has low photoelectric conversion efficiency for converting received light to an electric amount, and has large dark currents.
The light absorbing layer which absorbs light has such a small volume that the semiconductor laser has low photoelectric conversion efficiency for converting received light to an electric amount.
In such circumstances, an optical transmission and reception device having an optimum structure for the transmission and reception is needed.